Apparatus for indicating the position of a reference marker used in a gamma ray camera

ABSTRACT

Apparatus for indicating the position of a reference marker is adapted for use with a medical gamma camera. A movable reference marker is coupled to a fixed reference member by an arm, and x and y co-ordinate voltages are generated and fed to a display screen of the gamma camera to produce a reference mark on the screen corresponding to the position of the marker.

United States McCready et a1.

atent [451 May 30, 1972 [54] APPARATUS FOR INDECATING THE POSITION OF AREFERENCE 1 USED IN A GAMMA RAY CAIWERA Inventors: Victor RalphMcCready, Sutton; Sidney Patrick Newbery, London, both of EnglandNatlonal Research Development Corporation, London, England Filed: Apr.28, 1970 Appl. No.: 32,647

[73] Assignee:

Foreign Application Priority Data Apr. 30, 1969 Great Britain..22,140/69 US. Cl. ..250/83.3 R, 250/71.5 R, 315/26 Int. Cl. ..G0lt1/16, GOlt 1/20 Field of Search ..250/71.5 S, 83.3 R; 315/22,

1L Sin/ Cos 20 [56] References Cited UNITED STATES PATENTS 3,118,0851/1964 Clergue et a1 ..315/26 3,502,873 3/1970 Woronowicz........250/71.5 S 3,509,341 4/1970 l-lindel et a1. ..250/71 .5 S

Primary Examiner-Archie R. Borchelt Attorney-Cushman, Darby and Cushman[57] ABSTRACT 8 Claims, 3 Drawing Figures Lima VOLTAGE Put VULTABErnuowm FHLLBWER SCINTIBRAM & LUEIC 22 35 PULSE HEIGHT CIRCUITS XANALYSER (up GAMMA CAMERA) ISULATING Sin 6 VULTAEE FULLOWER x a v 3%,UEFLECTIUN macuns DIODE Patented May 30, 1972 3,666,952

2 Sheets-Sheet 1 Patented May 30, 1972 2 Shoots-Sheet 2 N a a was E 2:5252 mm a i APE m 25:; V w; 522 552E afia a 2 2 a :3 5:3 i 22 iv mw Rm 5 2=2 1% fimuw a 55% 5 Q w m 5 J I 522:: 533a 2553 I E I E; :1 5mm: 22,; 5$532 m EN m \5 g 2:2; 25: we: a 32 w i 25531 N E APPARATUS FORINDICATING THE POSITION OF A REFERENCE MARKER USED IN A GAMMA RAY CAMERAThe present invention relates to apparatus for indicating a referenceposition, and is concerned in particular, but not exclusively, withapparatus such as a gamma camera for produc ing visual images fromimages formed by radiation in a nonvisual wavelength range.

The gamma camera is well established as a reliable instrument forproducing visual displays of various organs, following the injection oflabelled compounds or radio-active isotopes. In routine clinical use,the instrument has the disadvantage, compared to the rectilinearscanner, of lacking the means of transferring accurately anatomicallandmarks to the gamma camera scintigram. The known technique of usingradio-active point sources as anatomical markers results in anill-defined area of brightness, which may be confused with radio-activeareas in the organ under examination. Also it is not possible totransfer to the display continuous lines such as a line indicating thelower edge of the rib cage.

According to the present invention y is provided apparatus forindicating the position of a reference marker comprising a fixedreference member, a movable reference marker coupled to the fixed memberin such a manner as to allow movement of the marker relative to themember in two orthogonal directions, and signal generating means coupledbetween the member and the marker, and arranged to generate a pair ofelectrical output signals which represent co-ordinates of the positionof the marker relative to the fixed member, and which are adapted to befed to a display system to indicate a reference mark on a displayscreen.

The pair of electrical signals may represent polar or cartesianco-ordinates.

Conveniently, the movable reference marker may be coupled to the fixedreference member by an arm such as to allow both angular and radialmovement of the marker by rotation and radial movement of the armrelative to the fixed member, the signal generating means being coupledbetween the arm and the fixed member.

The said generating means may comprise a linear potentiometer coupledbetween the arm and the fixed member and arranged to provide a voltageproportional to the distance between the marker and the fixed member,and a rotating potentiometer coupled to rotate with rotation of the armabout the fixed member and arranged to produce, for constant values ofthe said distance between the marker and the fixed member, a pair ofvoltages proportional respectively to the sine and co-sine of the angleof rotation of the arm, the two potentiometers being connected tocombine the linear and angular voltages to provide as the said pair ofelectrical signals a pair of voltages proportional respectively to theproduct of the said distance and the sine of the said angle, and to theproduct of the said distance and the co-sine of the said angle.

Thus a coordinate transfer system embodying the invention may use adisplay oscilloscope beam to draw lines or a cross on a Polaroid picturein the correct anatomical position in relation to the crystal surface.

There is also provided in accordance with the present inventionapparatus for producing visual images comprising means for detecting animage formed by radiation in a non-visual wavelength range, a displaysystem for displaying the said image as a visual picture on a displayscreen, and position indicating apparatus for generating a pair ofelectrical output signals which represent co-ordinates of a referenceposition in the field of view of the detecting means, the positionindicating apparatus being connected to feed the said output signalstherefrom to the display system to produce on the display screen, areference mark to allow correlation between features in the field ofview of the detecting means and features shown on the said visualpicture.

It will be appreciated that the electrical signals representingco-ordinates of the reference position to be displayed need not beproduced only by a reference marker coupled by an arm to the generatingmeans, but may be provided by other co-ordinate generating systems. Forexample, two linear potentiometers positioned orthogonally to provide aframe of reference in the field view of the gamma camera may be coupledto the reference marker by a pair of orthogonal arms which pick offdirectly x and y voltages representing the co-ordinates. The arms may becoupled to sliding taps on the linear potentiometer so as to allowmovement of the reference marker in two orthogonal directions.

Embodiments may be constructed as ancillary attachments to a camera andcan be removed completely in seconds, or moved to one side to permitchanging of collimators. The use of such apparatus does not impair thenormal circuit operation of the camera, and it can be connected in sucha way that a required rotation of the picture on the oscilloscope screenalso alters the reference points of the transfer system.

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of apparatus for indicating theposition of a reference marker, illustrating the geometricalrelationship between polar and cartesian co-ordinates;

FIG. 2 is a block circuit diagram of an electrical circuit for use withthe apparatus of FIG. 1; and

FIG. 3 is a perspective view of the apparatus of FIG. 1.

Referring to FIGS. 1 and 3, a movable reference marker 11 is coupled toa fixed reference member 12 by an arm 13. The arm 13 is free to rotateabout the member 12 and to move radially relative to the member 12 toallow the marker 11 to move in a plane perpendicular to the member 12.The plane of movement will normally be horizontal. The arm may also beprovided with a vertical adjustment by movement of the coupling meansvertically at the member 12, but such movement is not intended to bedetected by the present embodiment.

A linear potentiometer 14 is coupled between the arm 13 and the fixedmember 12, and is arranged to provide a voltage proportional to thedistance between the marker 11 and the fixed member 12. A rotatingpotentiometer 15 is coupled between the arm 13 and the fixed member 12and arranged to rotate with rotation of the arm 13. The rotatingpotentiometer 15 is arranged to provide, for a fixed value of thedistance between the marker 1 1 and the member 12, a pair of voltagesproportional respectively to the sine and co-sine of the angle ofrotation of the arm 13 relative to a fixed angular reference.

In use, with a gamma camera 16, the marker 11 is placed at a requiredanatomical landmark on the patient within the range 17 of the camera,and the voltages from the potentiometers l4 and 15 are applied (as willbe explained with reference to FIG. 2) to produce a visible referencemark on the visual display screen which normally displays a picturederived from the camera 16.

Referring to FIG. 1, the position of the marker 11 at point B relativeto a point A at the member 12 may be described by polar co-ordinates Land 6 where L is the distance between the points A and B and 0 is theangle of rotation of the arm 13 from an angular reference. The positionmay also be described in rectangular co-ordinates X and Y relative to apoint C at the center of the field of the camera 16, where X L Cos 0 ACand Y= L Sin 6. A voltage proportional to L is generated by altering thesetting of the linear potentiometer 14 and voltages proportional to LCos 6 and L Sin 9 are obtained from the rotating sine/co-sinepotentiometer 15 at the point A. A voltage proportional to AC, which isconstant, is added algebraically to the voltage proportional to L Sin 0.Thus voltage analogues proportional to X and Y can be fed to a displayoscilloscope normally displaying a picture from the camera 16.

For continuous lines such as the costal margin or the edge of a mass, atrain of pulses at approximately 10 kI-IZ is used for brighteningpurposes. Alternatively when single anatomical points are beingrecorded, a small deflecting voltage having a triangular waveform is fedalternately to the oscilloscope X and Y deflection amplifierssimultaneously with a train of brightening pulses. This produces a smallcross in the desired position.

Referring to FIG. 2, the output of the linear potentiometer 14 is fed toa voltage follower circuit 18. The output of the voltage followercircuit is fed directly to one terminal of the sine/co-sinepotentiometer 15 and is also fed through an inverter 19 to a secondterminal of the potentiometer 15. Voltages proportional to L cos 6 and Lsin are taken from the potentiometer and fed respectively to voltagefollower circuits 20 and 21. The outputs of the circuits 20 and 21 areamplified in amplifiers 22 and 23 respectively and fed to the x and ydeflection circuit 33 of the display device 34 which normally receivefrom the gamma camera scintigram 35 x and y coordinate signalsrepresenting features to be displayed. In known gamma cameras the x andy coordinate signals are produced by combining in logic circuits theoutputs of an array of photomultipliers behind the crystal of the gammacamera. The photomultiplier signals are also combined to give theso-called z-pulses which are proportional to the total energy of eachinteraction of radiation with the scintigram crystal. The z-pulses arefed to a pulse height analyzer 36 which selects the wavelength range ofradiation which is of interest and passes the appropriate z pulses tothe bright up circuit 37 of the display device 34. The image on thedisplay device 34 is then photographed by a photographic camera 38 overan exposure time for example between 1 and 4 minutes.

The circuit 37 controlling the brightening of the display device 34 canbe operated to indicate the position of the reference marker 11 in twomodes, by the production of continuous lines and crosses respectively.

A 10 kHZ pulse generator 24 is energized by closing a switch 25 and isconnected to feed negative going 3,us pulses (e. g. from 6 volts to 0volts) through an isolating diode 26 to the bright-up circuit 37 of thedisplay device 34. This connection simulates the z pulses from theanalyzer 36 and provides a train of pulses needed to produce referencelines on the display device.

Continuous lines are formed by following lines on the patient with amarker 11 and depressing the switch 25 so that a continuous train ofbright-up pulses produces in effect a continuous line on the displayoscilloscope of the gamma camera. This is used when it is required todraw circles or straight lines, or outline various parts of the patient.Although the lines are continuous in the sense that they are notinterrupted during drawing, they are instantaneous unless storagefacility is provided in the display system.

A second switch 27 energizes a further switching circuit 28 comprising asquare wave generator which controls a gate driver circuit 29. The gatedriver circuit 29 opens alternately two gates 30 and 31 to which areapplied signals from a triangular waveform generator 32. The outputs ofthe gates 30 and 31 are connected to second inputs of the amplifiers 22and 23 respectively and operate in the second mode of the apparatus forproducing crosses on the display device 34. Thus when the switches 25and 27 are both closed, the brightening pulses are applied as above inthe first mode, but in addition, a triangular waveform is fedalternately through the gates 30 and 31 to the X and Y amplifiers 22 and23, thus providing the deflection voltages to form a cross which is usedto mark the required anatomical point on the display device 34.

In use, the device is calibrated initially by placing collimatedradioactive sources at the edges and center of the crystal which issensitive to the gamma rays and which lies within the detector head ofthe gamma camera 16 behind the lead collimator. The gain and shiftsettings of the apparatus are then adjusted so that the position of themarks generated by the apparatus are coincident with the images of thesources. For accurate operation of the apparatus, the gain of the cameraamplifiers must remain constant. Periodic use of the calibratingprocedure outlined above is used to detect any departure from normal.

During use of the apparatus of FIG. 2 to provide reference marks on thedisplay device 34, the output from the scintigram 35 is entailed and thecamera 38 is left on. Although the generation of a straight line, say,in the first mode, does not produce a stored image on the display device34, a stored line is recorded at the camera 38 due to the relativelylong exposure time.

To operate the device after calibration, the detector 16 is retracted afew inches from the patient, the arm 13 is tilted slightly downwards,and the marker 11 is placed over the desired position on the patient.

The apparatus described is suitable for use with a parallel collimatorin the detector head 16, as the magnification of the image isindependent of the distance of the camera from the object observed. Inthe case of a pin-hole collimator, however, the magnification of theimage is inversely proportional to distance between the camera and theobject. Since the relationship between movements of the probe 1 1 andmovements of the reference mark on the screen are constant, thereference mark would no longer be accurately positioned. This difficultyis overcome in a modified embodiment of the invention (not shown) inwhich a variable gain inverting amplifier is connected before thevoltage follower 18. A correction factor to be applied to this amplifieris then worked out using a template of say an inch square of metal atvarious distances from the camera. The gain of the inverting amplifieris then varied inversely with the camera to object distance to ensurethat movements of the reference mark on the display are in proportion tofeatures of the field of view magnified by the camera 16.

We claim:

1. Apparatus for producing visual images comprising means for detectingan image formed by radiation in a non visual wavelength range, a displaysystem for displaying the said image as a visual picture on a displayscreen, and position indicating apparatus for generating a pair ofelectrical output signals which represent coordinates of a referenceposition in the field of view of the detecting means, the positionindicating apparatus being connected to feed the said output signalstherefrom to the display system to produce on the display screen, areference mark to allow correlation between features in the field ofview of the detecting means and features shown on the said visualpicture.

2. Apparatus according to claim 1 in which the position indicatingapparatus comprises a fixed reference member,

a movable reference marker coupled to the fixed member in such a manneras to allow movement of the marker relative to the member in twoorthogonal directions, and

signal generating means coupled between the member and the marker, andarranged to generate a pair of electrical output signals which representco-ordinates of the position of the marker relative to the fixed member,and which are adapted to be fed to a display system to indicate areference mark on a display screen.

3. Apparatus according to claim 2 in which the movable reference markeris coupled to the fixed reference member by an arm such as to allow bothangular and radial movement of the marker by rotation and radialmovement of the arm relative to the fixed member, the signal generatingmeans being coupled between the arm and the fixed member.

4. Apparatus according to claim 3 in which the said generating meanscomprises a linear potentiometer coupled between the arm and the fixedmember and arranged to provide a voltage proportional to the distancebetween the marker and the fixed member, and a rotating potentiometercoupled to rotate with rotation of the arm about the fixed member andarranged to produce, for constant values of the said distance betweenthe marker and the fixed member, a pair of voltages proportionalrespectively to the sine and co-sine of the angle of rotation of thearm, the two potentiometers being connected to combine the linear andangular voltages to provide as the said pair of electrical signals apair of voltages proportional respectively to the product of the saiddistance and the sine of the said angle, and to the product of the saiddistance and the cosine of the said angle.

5. Apparatus according to claim 1 including means for adding to each ofthe said output signals a periodic triangular waveform arranged togenerate in operation a cross as the 5 reference mark on the saiddisplay screen.

6 Apparatus according to claim 2 including means for supplying, inoperation, to the said display system, a series of periodic pulses tocontrol brightening of the display screen so as to produce a continuousline when the reference marker is l0 moved relative to the fixedreference member.

7. Apparatus according to claim 1 in which the said detecting meanscomprises a gamma camera for medical use.

8. Apparatus according to claim 1 including means for forming a storedimage of the picture and means for inhibiting the display system fromdisplaying a picture from the detecting means while the positionindicating apparatus is energized to produce the said reference mark onthe said display screen

1. Apparatus for producing visual images comprising means for detectingan image formed by radiation in a non visual wavelength range, a displaysystem for displaying the said image as a visual picture on a displayscreen, and position indicating apparatus for generating a pair ofelectrical output signals which represent coordinates of a referenceposition in the field of view of the detecting means, the positionindicating apparatus being connected to feed the said output signalstherefrom to the display system to produce on the display screen, areference mark to allow corrElation between features in the field ofview of the detecting means and features shown on the said visualpicture.
 2. Apparatus according to claim 1 in which the positionindicating apparatus comprises a fixed reference member, a movablereference marker coupled to the fixed member in such a manner as toallow movement of the marker relative to the member in two orthogonaldirections, and signal generating means coupled between the member andthe marker, and arranged to generate a pair of electrical output signalswhich represent co-ordinates of the position of the marker relative tothe fixed member, and which are adapted to be fed to a display system toindicate a reference mark on a display screen.
 3. Apparatus according toclaim 2 in which the movable reference marker is coupled to the fixedreference member by an arm such as to allow both angular and radialmovement of the marker by rotation and radial movement of the armrelative to the fixed member, the signal generating means being coupledbetween the arm and the fixed member.
 4. Apparatus according to claim 3in which the said generating means comprises a linear potentiometercoupled between the arm and the fixed member and arranged to provide avoltage proportional to the distance between the marker and the fixedmember, and a rotating potentiometer coupled to rotate with rotation ofthe arm about the fixed member and arranged to produce, for constantvalues of the said distance between the marker and the fixed member, apair of voltages proportional respectively to the sine and co-sine ofthe angle of rotation of the arm, the two potentiometers being connectedto combine the linear and angular voltages to provide as the said pairof electrical signals a pair of voltages proportional respectively tothe product of the said distance and the sine of the said angle, and tothe product of the said distance and the co-sine of the said angle. 5.Apparatus according to claim 1 including means for adding to each of thesaid output signals a periodic triangular waveform arranged to generatein operation a cross as the reference mark on the said display screen.6. Apparatus according to claim 2 including means for supplying, inoperation, to the said display system, a series of periodic pulses tocontrol brightening of the display screen so as to produce a continuousline when the reference marker is moved relative to the fixed referencemember.
 7. Apparatus according to claim 1 in which the said detectingmeans comprises a gamma camera for medical use.
 8. Apparatus accordingto claim 1 including means for forming a stored image of the picture andmeans for inhibiting the display system from displaying a picture fromthe detecting means while the position indicating apparatus is energizedto produce the said reference mark on the said display screen.